I am thinking O2 sensor, how about you! | Ford Explorer Forums - Serious Explorations

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I am thinking O2 sensor, how about you!


Well-Known Member
January 7, 2004
Reaction score
City, State
Pepperell, MA
Year, Model & Trim Level
'05 XLT V8
My 05 Ex with the 4.6 started to idle rough today. Ran fine yesterday. Then after a stop at the mall on the way home the MIL came on. I was hoping for a misfire code but was not so lucky. I retrieved the following. P0174 and P2197. Bank 2 lean and Lack of HO2s- B2S1 Switching, Sensor indicated lean. The code reader said B2S1 stuck. The following snap shot data was obtained:

Engine coolent temp: 185
Short Term Fuel Trim - Bank 1: -0.78%
Long Term Fuel Trim - Bank 1: 0.78%
Short Term Fuel Trim - Bank 2: 29.69%
Long Term Fuel Trim - Bank 2: 24.22%
Intake Manifold Absolute Pressure: 15.99 inHg
Engine RPM: 1552.25 RPM
Vehicle Speed: 17.40 MPH
Ignition Timing Advance #1 Cylinder: 36.50
Intake Air Temp: 78.80
Air Flow Rate MAF Sensor: 2.69 lb.min
Absolute Throttle Possition: 20.78%
Oxygen Sensor Output Voltage (B1-S1): 0.65v
Oxygen Sensor Output Voltage (B1-S2): 0.49v
Short Term Fuel Trim (B1-S1): 0.78%
Short Term Fuel Trim (B1-S2): 99.22%
Oxygen Sensor Output Voltage (B2-S1): 0.01v
Oxygen Sensor Output Voltage (B2-S2): 0.77v
Short Term Fuel Trim (B2-S1): 28.91%
Short Term Fuel Trim (B2-S2): 99.22%
Time Since Engine Start: 162 sec
Fuel Rail Pressure relative to Vacuum: 38.88 PSI
Commanded EGR: 43.14%
EGR Error: 16.41%
Commanded Evaporative Purge: 0.00%
Fuel Level Input: 58.82%
Warm ups since DTC Cleared: 255
Distance since DTC Cleared: 25850.86 miles
Evap System Vapor Pressure: -32.65 inHg
Barometric Pressure: 29.91 inHg
Catalyst Temp Bank 1: 1126.76
Catalyst Temp Bank 2: 1126.76

Looking at the Bank 2 numbers I would say that the B2-S1 needs replacement. I looked for broken or dislodged vacuum lines and could not find anything out of place.

What do you all think?


I see a lot of P1074 and P1071 at work and it is usually a MAF versus an oxygen sensor. If you get both it's almost always that MAF. There's a pretty easy way to tell if it is the MAF or not. Just go over by your air filter and you should find the MAF sensor plugged in along your air intake. Unplug it and leave it for a minute or two, then plug it back in. If it begins rough idling or even dies when you plug it back in, that is most likely your culprit. Otherwise if you see no change I would look into that oxygen sensor.

Because I was only getting P0174 (Bank 2 lean) and not P0171 (lean bank 1) along with it, I ruled out the MAF or vacuum leak. The P2197 (B2S1 O2 sensor Stuck) along with the freeze frame data lead me to believe either the sensor was bad or in fact that bank 2 was running lean; indicating a fuel delivery issue with the bank 2 rail. I took a stab at the bank 2 upstream sensor and happened to be right. So for $97 I replaced it and reset the MIL. Now it runs great. A friend of mine even said that my Ex seems to be running smoother and starts better now. I hadn't told him that I replaced the sensor. I am even getting much better fuel economy now. I surmise the sensor was going bad for a while and finally gave up the ghost.